1. Field of the Invention
The present invention relates to a CATV circuit with an automatic noise controller and a CATV system using such CATV circuit, and more particularly to a CATV circuit with an automatic noise controller and a CATV system using the CATV circuit to automatically reduce upstream noises in a CATV circuit for bidirectional communications between a control center and a home terminal.
2. Description of the Related Art
In general, the network of a CATV system is tree-structured, and noises produced by home terminals are loaded onto the network through an upstream circuit of a control center. The noises produced by the home terminals are gathered and cause interferences to normal signals, and thus a normal communication cannot be conducted occasionally. Such noise is generally called an “upstream noise”. To assure a normal communication, it is necessary to suppress the source of upstream noises, which refers to a noise generating source including short waves of a frequency band of the aforementioned upstream circuit or a spurious signal produced by components of an electric appliance such as a refrigerator or a vacuum cleaner.
In the past, a control center with a broadcasting function is connected with a plurality of transceivers in a tree structure through a CATV network for executing bidirectional communications in a CATV system. A CATV circuit having a stream noise discovered at an early stage over the network is disconnected to prevent a poor communication caused by the upstream noises. In the methods of detecting a stream noise in an upstream circuit as described in the cited patents, an upstream noise transmitted from the transceiver to the control center and occurred at each transceiver can be detected, if the stream noise level exceeds a predetermined threshold.
In the aforementioned prior art, the upstream circuit will be disconnected if the stream noise exceeds a predetermined threshold, so that any adverse effect of the upstream noises on other home terminals can be eliminated by simply reducing the upstream noise level of the detected noise portion of the upstream circuit at an upstream end. However, the home terminal with a disconnected upstream circuit no longer can execute the bidirectional communications. Particularly for an apartment complex having many home terminals at the downstream of the disconnection, these home terminals will be affected significantly by the disconnected upstream circuit.
In view of the shortcomings of the prior art, the present invention provides a CATV circuit with an automatic noise controller and a CATV system using the CATV circuit, such that if a noise level exceeds a predetermined threshold, a portion of the CATV system exceeding the noise level can still hold the bidirectional communication to minimize the adverse effects brought by a disconnection of the upstream circuit.